1. as for和as to均可用於句首，此時是在更換話題。
As for the journey, we will decide that later.
As for myself, I am not satisfied.
I feel that there's a lot of pressure put on policemen. And as for putting guns in their hands, I don't think that's a very good idea at all.
He said nothing as to which was the stronger.
He said nothing as to when he would come.
Nobody could decide (as to) what to do.
Classify butterflies as to size and color.
Andy sat down at the table and inquired as to what the problem was.
2. If you compare one person or thing to another, you say that they are like the other person or thing.即你在做類比（即xxx與xxx相同）。
I can only compare the experience to falling in love.（這個經驗我認為只有戀愛可以與其相類比；即它跟戀愛相同）
If you say that something does not compare with something else, you mean that it is much worse.（比較差）
The flowers here do not compare with those at home.這裡的花比不上家裡的。
If one thing compares favorable with another, it is better than the other thing. If it compares unfavorable with another, it is worse than the other thing.（比較好，或比較差）
2014-07-24 11:36:09 補充：
Traditionally, "compare to" is used when similarities are noted in dissimilar things: shall I compare thee to a summer's day? "To compare with" is to look for either differences or similarities, usually in similar things: compare the candidate's claims with his actual performance.
2014-07-24 11:38:41 補充：
In practice, however, this distinction is rarely maintained.
New Oxford American Dictionary
third edition 2010
2014-07-26 19:54:30 補充：
"To compare with" is to look for either differences or similarities, usually in similar things:
"to compare with"通常是用在相似的東西上，來看它們的不同或相同點。
"To compare to"則是用在相異的東西上，來看它們的相同點。
Collins Cobuild English Dictionary for Advanced Learners